This is my attempt at making a trampoline as realistic as possible:

I went outside and took around 50 photos of a real trampoline including textures for the jumping mat (I would have loved to upload a few of them here but blenderartists only allows 3 images per post)

It has all the springs and details of a real one:

I removed the cover in this render so you can take a closer look at it:

A recorded the entire process as a Speedart, so you can take a colser look at how I made it:

I also put it on Blendswap:

And it’s on sketchfab: